1. Field of the Invention
This invention relates generally to chemical mechanical processing of semiconductor wafers, and more particularly concerns a method and apparatus for recovery of components of an aqueous chemical mechanical abrasive slurry containing finely divided, suspended particles following their use in processing of semiconductor wafers. The invention herein relates specifically to an apparatus for diverting flow in a waste stream into clean and turbid components.
2. Description of Related Art
Semiconductor components are commonly manufactured by layering electrically conductive and dielectric materials to achieve appropriate electrical characteristics for fabrication of multiple electrical components such as resistors, capacitors and transistors. Many of these discrete devices are incorporated into integrated circuits for use in creating microprocessors, memory devices, logic circuits, and the like. Many integrated circuits can be produced on semiconductor wafers by layering of dielectric and electrically conductive materials to create multiple semiconductor devices in a relatively small area.
The density of electrical components and interconnect wiring on such semiconductor devices has continually increased as trace line widths on such semiconductor devices have narrowed. At one time, for example, trace line widths on such devices typically ranged from 1 xcexcm to 4 xcexcm. However, in recent years, the industry has made significant advances in reducing trace line widths used in creation of integrated circuits to less than 1 xcexcm. Currently, trace line widths of 0.18 xcexcm to 0.25 xcexcm are common, and research is being done to achieve trace line widths of from 0.15 xcexcm to 0.18 xcexcm. In addition, the demand for increased memory and computing power has driven the limits on the number of semiconductor devices per integrated circuit that are achievable ever higher, resulting in an increase in the number of layers applied to semiconductor wafers, while the typical size of the integrated circuits continues to decrease. The combination of narrower trace line widths, increased layers of materials and higher densities of semiconductor devices per integrated circuit has made such devices increasingly susceptible to failure due to inconsistencies on semiconductor wafer surfaces, and it has become increasingly important that such semiconductor wafers have surfaces and dielectric layers that are uniformly smooth.
Methods for chemical mechanical planarization (CMP) have been developed to polish the surface of semiconductor wafers, and typically involve rotating the wafer on a polishing pad, applying pressure through a rotating chuck, and supplying an aqueous chemical slurry containing an abrasive polishing agent to the polishing pad for both surfactant and abrasive processing. Abrasive agents that can be used in the chemical mechanical slurry include particles of fumed or colloidal silica, ceria, and alumina. The chemical mechanical slurry can also include stabilizer or oxidizer agents. Silica is typically mixed with a stabilizer such as potassium hydroxide or ammonium hydroxide, and is commonly used to polish dielectric or oxide layers on the semiconductor wafer. Ceria and Alumina are commonly mixed with an oxidizer agent such as ferric nitrate or hydrogen peroxide, and are typically used to polish metal layers, such as tungsten, copper and aluminum, for example.
The slurry and material removed from the various layers of the semiconductor wafer form a waste stream that is commonly disposed of as industrial waste. The abrasive components constitute approximately 8% to 15% by weight of the process CMP slurry, with the remainder constituting other chemical agents such as stabilizer or oxidizer agents, and water. The raw waste stream is typically diluted with other process deionized (DI) water in the CMP polishers to yield a final solids concentration of 0.2% to 1.0% by weight in the waste stream. However, the disposal of dissolved or suspended solids in the industrial waste stream has become a relevant issue due to strict local, state and federal regulations, and it would thus be desirable to provide a process and apparatus to remove abrasive components from the waste stream for possible removal of heavy metal components for separate disposal.
Since, for a significant amount of time, the waste stream contains only DI water containing little, in any, contaminants; it would also be desirable to recover as much of this water as possible to permit reuse of the water in the chemical mechanical planarization process. Ideally, this reclaim process would occur at the polisher tool in order to effectively reuse the DI water and simultaneously save costs. While conventional filtration technology exists for point-of-use filtration, this technology is not suited for the high probability of suspended matter in the waste stream. With conventional filtration, all effluent flow is into the filter at a perpendicular angle to the membrane element. The particles embed in the membrane media and the filter subsequently clogs. This causes high downtime and related operating costs.
Alternatives to point-of-use filtration include central plant treatments such as pH neutralization and the addition of flocculating or settling agents in conjunction with filter presses; ultrafiltration or reverse osmosis filtration systems. These systems represent a prohibitively costly system for users with just several polishing tools and continuing high operation costs. Further, these systems are gravity drain based. Because of the nature of the suspended solids in the slurry effluent, and the common practice of combining waste streams at a central point prior to treatment, any clear waste collected is sufficiently mixed with particulate bearing fluid as to require treatment of the entire waste stream. It is therefore desirable to have a process which recovers the usable water from the process and eliminates the primary suspended particles problem near the point of origination of the waste stream, yet is flexible enough to meet slurry specific problems. It is also desirable to have a process that is scalable from pilot production to full scale manufacturing. The present invention meets these needs.
Briefly, and in general terms, the present invention provides for the separation of abrasive components and clear fluids from an aqueous chemical mechanical slurry used for planarization of semiconductor materials, to permit the reuse of the clear liquid effluent in non-process applications as well as for gray water for irrigation, process cooling water, or as make-up water for a reverse osmosis system, or safe disposal in the industrial waste stream, as desired. With the additional use of continuous ion exchange, the resulting water stream can be reused in high purity water applications.
The invention accordingly provides for a method and apparatus for recovering clear liquid from an aqueous slurry waste stream and for concentrating particles of abrasive materials from the same aqueous solution. In one presently preferred embodiment, the apparatus comprises a solids detection device for detecting the concentration of abrasive solids in the aqueous waste stream. The solids detection device preferably receives raw waste including the aqueous slurry containing abrasive particles and materials removed from planarization of semiconductor materials from the polishing tool, and is preferably located in a location of close proximity to the polishing tool. The solids detection device may optionally also detect other materials, and may also optionally measure incoming flow, effluent conductivity, temperature, turbidity, and/or pH. In a presently preferred embodiment, the sensor is of the type which detects solids concentration using light scattering turbidity measurements, combined with conductivity and temperature measurements. A diverter receiving the effluent flow from the solids detection device is also provided for diverting the entire effluent stream including the aqueous slurry containing abrasive particles and materials removed from planarization of semiconductor materials to at least one reuse water collection tank when the abrasive solids concentration is below a desired threshold, and to at least one concentrate water collection tank when the abrasive solids concentration is greater than or equal to the desired threshold.
In a first presently preferred embodiment, the diverter comprises a displaceable conduit and a piston cylinder connected to the displaceable conduit by a collar. The piston cylinder is controlled by the solids detection apparatus, and the displaceable conduit is moveable between first and second positions, such that when the solids concentration is above a desired threshold, the solids detection apparatus causes the piston cylinder to move to the first position, directing the displaceable conduit outlet to the one or several concentrate water collection tanks, and when the solids concentration is below a desired threshold, the solids detection apparatus activates the piston cylinder to move to the second position, in which the displaceable conduit diverts the clear liquid of the effluent to the one or several reuse water collection tanks. In a preferred aspect of the invention, the displaceable conduit comprises a flexible hose.
In another presently preferred embodiment, the diverter comprises a valve housing having an inlet, a first outlet for diverting flow to the one or several concentrate water collection tanks, and a second outlet for diverting flow to the one or several reuse water collection tanks. A solenoid is connected for control by the solids detection apparatus, and is connected to a valve piston movable between first and second positions, the valve piston having a first channel for diverting flow to the first outlet in the first valve piston position, and having a second channel for diverting flow to the second outlet in the second valve piston position. In a presently preferred modification, the diverter can further comprise a safety connected to the inlet of the diverter.
In another presently preferred embodiment, the diverter comprises a valve housing having an inlet, a first outlet for diverting flow to the one or several concentrate water collection tanks, and a second outlet for diverting flow to the one or several reuse water collection tanks. A solenoid is connected for control by the solids detection apparatus, and is connected to a valve piston movable by the solenoid between first and second positions, the valve piston blocking flow to the second outlet for diverting flow to the first outlet in the first valve piston position, and blocking flow to the first outlet for diverting flow to the second outlet in the second valve piston position.
In a presently preferred aspect of the apparatus of the invention, a pump can be provided for directing the reuse water for reuse as non-process equipment rinse water, or as process water in non-critical rinsing applications in the polishing tool, or for other applications. Optionally, the reuse water can be subjected to an ion exchanger for an ion exchange treatment prior to reuse in process applications. In another preferred aspect, a source of deionized water may be provided, for directing deionized water to the polisher, such as when adequate reclaimed water is not available from collection tanks.
In a presently preferred embodiment a pump can also be provided for directing the concentrate water from the concentrate water collection tanks to a concentrator apparatus which further separates the clear liquid component from the abrasive solids and concentrates the abrasive solids for disposal. In one preferred aspect, means are provided for directing clear liquid from the concentrator apparatus for reuse, or to an industrial waste treatment system for disposal.
In the method of the invention, an aqueous slurry waste stream which, on an irregular basis, contains an abrasive component, is introduced into a particle detection device which uses one of several technologies to detect the presence of abrasive particles. The detection device may use optical, ultrasonic or other similar detection techniques to measure the density of the abrasive solids in the effluent stream. Based on the measurement made by the detection device, when solids concentrations below a desired threshold are indicated, the effluent stream is diverted by way of a diverter to one or several small reuse water collection tanks. The collected liquid is pumped back to the polisher through an apparatus which provides non-process water to the polisher for reuse as rinse water. Further, when used in conjunction with ion exchange technologies, including resin beds and continuous ion exchange, or elutriation to achieve high quality deionized water, the water stream may be diverted to high purity, process water applications. Alternatively, when a solids concentration over the desired threshold is detected, the entire waste stream is diverted by way of a diverter to one or several small concentrate water collection tanks. The collected concentrate is motivated under pressure to another device for further concentration and processing. This apparatus is capable of concentrating the polisher waste stream from as little as 0.2% solids by weight to as high as 4% solids by weight without additional filtration or waste treatment means.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.